Electron discharge device



Feb. 20, 1940. N, M RUST ET AL 2,190,735

ELECTRON DISCHARGE DEVICE Filed Feb. 2, 1938 -"lrlnalrallllpzrlrlrllnurlf INV EN TORS NOEL MEYER RUST/mo BY GEUGE FRB URN BRETT @WCM ATTORNEY.

5 electrode.

Patented Feb. 2.0, 1940 irre 2,190,735 essere@ ,alsmaar DEVICE Ncl-lilleyer-Rust, Chelmsford, and l Georgev Fairbnrn Brett, Londen, England, assignors to Radio Corporation of America, a 'corporationof Delaware Application February 2,1938, lSerial No. 188,244

in Great Britain February 't 1.9.37

4 Claims.

This invention, which is for improvements in or modiiications of the invention contained in ourco-pending application No. 115,279 filed Decernber 11,1936; relates to electron discharge devices, more `particularly to such devices of the fso-callecl electron beam typeQi. e., of the type vWlfrerein the electron discharge partakes more of 0 so positioned that'the amount of cross section of thebe'am intercepted by the anode may be varied by ldeflectingI the beam or by varying its cross section at the anode; any portion of thecbeam not intercepted bythe anode falling on rthe collector t The 'valve' may include means for dele'cting thebearn` transversely of the anode.

4""lll'inong the important advantages obtainable from electron beam tubes as described in the copending application is that it is possible to obtain anode voltage-anode current characteristic y curves which become substantially dat from relatively small vvoltages-say about l50 voltsupwards even with anode currents as high as 30- 40 milliamperes.

Among the constructions described in our copending application are constructions whereby `these characteristic'curves may be caused to have ,Ilgative slopes the modus operandi of these constructions depending on the obtaining of a change'in the size of the cross sectional'area of the electron beam at the slotted anode (behind which is the collector electrode) as the voltage on the anode is changed. `Our co-pending application illustrates "such a construction wherein negatively sloping characteristics are obtained with' this type "of focussing control action.

The principal object of the present invention is to provide an electron discharge device of the beamtype' having negatively sloping characterstics which may be either of very slight slope or of very steep slope.

` The novel features which We believe to be characteristic of our invention seU forth With particularity in the appended claims, but lthe invention'itself will best be understood by refertion.

ence tothe following description'taken in 'con'- nection with theaccornpanying drawing in which Figures 1 and y2 are ,diagrammatic representations ofonerorm of anelectron discharge device embodyingvolv'ir invention under different voltage conditionsgand Figures `3 and fl are diagrammatic representatwonsy of modifications of an electronldischarge device embodying our inven- 'Infcertain circuit arrangements, for exampleinradio receiver circuits Where Vhigh selectivity is required; it is frequently advantageous to obtain anoperating anode voltage-anode current curve v/ith avery slight negativeslope over' the whole curve betweensay 50. vo`ltsand 250 volts. For other cases very steep negative slopes may be required. Thelarrangements described in our copending applicationvvhilegiving negatively sloping'charactristies, are not Well adapted to give either very slightnslopes'orvery steep slopes, nor isv 'it possible 4to easily controlthe amount'of slope.

Where Aa yslight negative slope is required the tube (according to the present invention) is providedfwith a slotted anode in which the slot is substantially smaller insize than `the slots inthe ,other ,SlQted electrodes ofthe valve, For example theslot in the slotted anode may be inade `of relatively vshort length Aor `it may be replaced A circular aperture of 'by a circular aperture. about 0.5"to about `l `millimeter in diameter is approximately equivalent yin results to a short slotabout 1 to 2 millimeters long and about 0.5 millimeter Wide.` lIn generalthe useof a circular apertiuje placed at any point along the approxi.-

mate electron beam line focus on the slotted anode is' satisfact'oryf- The result of using a small slot or .aperture in the slotted anode is that jvhile the 'change of focus which occurs as the anqd ,Volt increases' causes more and more current tormisnsthe rslotted anode and pass to the collector electrode, owing to the'small size of the aperture in the slotted modey only a small a'mountoi fcurrent Will ,be by-passed for a relatively large change in anode voltage. In pract tice thecollector anode should be maintained at a permanently higher voltage than the apertured or slotted. anode in order to prevent the return or secondary electrons'to the said apertured or slottedlanode.

In Figures' l and 2 are similar schematic views or" one forni' of valve in accordance with this invention and adapted to give a small negative slope to the anode voltage-anode current characteristic'."`1n"'these figuresthe electron beams are represented in `conventional manner by broken lines, Figure 1 showing the eiect with a high anode voltage and Figure 2 showing the efrect with a low anode voltage; In these :figures the electron gun comprises a cathode l, a controly electrode 2, an accelerator anode 3, ,a screen suppressor electrode'd, an anode 5 Whose slot 6 is, in

' yaccordance with this invention, made of subvstantially smaller size than the slots 1, 8, 9, in the other slotted electrodes 2, 3, 4 respectively, and nal collector electrode I0. In both Figures 1 and 2 the lengths of the slots extend perpendicularly tothe plane of the drawing. n

Where negative sloping -characteristics of large controllable negative slope are required the tubes are designed to rely for their operation more upon space charge considerations than upon beam focussing Where a steep negative sloping characteristic is required the electron beam tube is (according to this invention) provided with a vsuppressor electrode which is slotted or apertured and is positioned between the slotted lor apertured anode and the collector electrode.

In Figure 3 is shown a tube of this kind. I-Iere,

as before, the electrode system consists of a cathode l a slotted control electrode 2,`with al slot 1, a slotted accelerator anode 3 with a slot l8v and a slotted screen suppressor electrode 4 with a slot S, all of these electrodes being known per se in electron beam tubes. `The electrodes are arranged'in succession in the order stated close to one another withtheir apertures in 'register so vthe slotted anode 5, a second screen suppressor electrode Il in the form of a plate with a slot I2 the said slot l2 being of approximately thesame length as the slots in the other slotted electrodes but being Wider than the slot 6 in the adjacent slotted anode 5.

In use the lsecond suppressor electrode Il is maintained at or near cathode potential and normal operating potentials are applied to all the other electrodes. The action of the second suppresser electrode Il is to prevent electrons which have passed through the slot 6 in the slotted anode 5` to the. collector electrode l0 yreturning to said slotted anode 5. `In other words, the second suppressor electrode permits of quite low potentials being applied to the collector electrode l without any risk of secondary electrons returning .to the slotted anode 5 which may be at an operating potential -say between 50 and 250 volts. Nevertheless not all the current reaching the aperture 6 in the'slotted anode 5 necessarily passes on to the collector electrodev l because of space charge limitations in the space between these two electrodes. These space charge limitations depend on- (a) The beam current at the slot in the slotted anode 5.

(b) The potential of the slotted anode 5.

(ic) The potential of the collector electrode l0.

(d) The separation between the slotted anode Y and the collector electrode I0, and

(e) The potential on the second suppressor electrode ll. y In practice, with the second suppressor electrode Il at cathode potential, the collector electrode l0 at 5 to 100 volts, and the separation between 'these two electrodes at 2 to 5 millimeters, it is found that large currents will pass to the collector electrode I0 only when high potentials are applied to the slotted anode 5. At low values of slotted anode potential, the space charge causes .much of the current to pass to the said slotted anode 5 and hence'the current to this anode 5 falls as its potential rises and vice versa.

It is found that by varying` the potential onthe collector electrode vlll the steepness of the negative slope of the anode voltage-anode current these two actions in conjunction, quite steep negative slopes'can be obtained without (it will be observed) depending in anyway upon unreliable or irregular secondary emission effects.

The various slotted electrodes .employed in' valves in accordance with this invention need not be, as they are in Figures 1, 2 and 3 all in the form of slotted flat plates, for other forms of slotted electrodes may be used, either in the gun or elsewhere. For example, the accompanying Figure 4` .shows a valvewhich is like that of Figure 3V except that the collector electrode l0 is within a cylindrical second screen suppressor electrode I-I having a slot I2', this electrode being in turn.

within on anode 5 which is also of .cylindricall`l`35 form and has a slot 6'. In each ca se the` elecy trodes vare enclosed by an envelope I3.v

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed,

it will be apparent' that our invention is by no means limited to the exact forms illustrated or l the use indicated, but thatfmany variationsmay be madein the particular structure used and the purpose for which it is employed without-departing from the scope of `our invention as set forth Vin the appended claims.

including a control grid, an accelerating grid, and' a screen grid positioned between the cathode and the apertured anode, all of said electrodes.- being vpositionedlwith the apertures in alignment, and

an apertured suppressor electrode positioned between the apertured anode and the collector electrode. v

2. An electrondischarge device having acathode for emitting electrons and an apertured anode for receiving ,saidk electrons, and a co1- lector electrode on the sideof the anode opposite from said cathode, and a plurality of. apertured electrodes including a control grid,'an accelerating grid and a screen grid positioned between the cathode and the apertured anode, all of said electrodes being positioned with the `apertures in alignment, and an apertured suppressor electrode positioned between the apertured vanode and the collector electrode, the `suppressorelec- 'trode being closer to the apertured anodethan to said collector electrode.

3. An electron discharge device having a cathode for emitting electrons and an aperturedy if, 4. An electron discharge device comprising a cathode for emitting electrons, and an anode electrode comprising a iiat apertured plate and a collector electrode on the side of the anode opposite the cathode and in registry with the aperture in the anode, a flat control electrode, a at accelerating electrode and a flat screen electrode mounted in succession from the cathode to the anodeand provided with apertures aligned With the aperture in the slotted anode, and a suppressor electrode comprising a at electrode having an aperture of larger size than the aperture in the anode and aligned with the aperture in the anode.

NOEL MEYER RUST. GEORGE EAIRBURN BRETT. 

